Imaging devices are used to produce machine-readable data which is representative of the image of an object, e.g. a page of printed text. One type of imaging device is a photoelectric imaging device. As used herein, the phrase “photoelectric imaging device” means any device that generates data representative of an imaged object through use of a photosensor array such as a charge coupled device (CCD). Examples of photoelectric imaging devices include devices such as camcorders and digital cameras which instantaneously focus an entire image which is to be captured onto a two-dimensional photosensor array. Another example of a photoelectric imaging device is a line-focus system.
Some line-focus systems image an object by sequentially focusing narrow “scan line” portions of the object onto a linear photosensor array by sweeping a scanning head over the object. Examples of such devices, commonly referred to as optical scanners, include computer input devices usually referred to simply as “scanners” as well as facsimile machines and digital copy machines.
A line-focus system is also used in some barcode readers. Generally, in line-focus barcode readers, a narrow portion of a barcode is imaged onto a linear photosensor array. Electrical output from the photosensor array may then be analyzed to read the imaged barcode. Examples of imaging devices that are useable in conjunction with barcode readers are disclosed in U.S. Pat. No. 6,118,598 of Gardner, Jr. for METHOD AND APPARATUS FOR SETTING FOCUS IN AN IMAGING DEVICE and in U.S. patent application Ser. No. 09/290,216 filed on Apr. 13, 1999, of Gardner, Jr. for ALIGNMENT APPARATUS AND METHOD FOR AN IMAGING SYSTEM, which are both hereby specifically incorporated by reference for all that is disclosed therein.
In a line-focus system, a light beam from an illuminated line object is imaged by a lens onto a linear photosensor array which is positioned remotely from the line object. The linear photosensor array is a single dimension array of photoelements that correspond to small area locations on the line object. These small area locations on the line object are commonly referred to as “picture elements” or “pixels.” In response to light from its corresponding pixel location on the line object, each photosensor pixel element in the linear photosensor array (sometimes referred to simply as “pixels”) produces a data signal that is representative of the light intensity that it experiences during an immediately preceding interval of time known as a sampling interval. All of the photoelement data signals are received and processed by an appropriate data processing system.
In a color optical scanner, a plurality of spectrally separated imaging beams (typically red, green and blue beams) must be projected onto a photosensor array or arrays. The construction and operation of color optical scanners is fully disclosed in the following U.S. Pat. No. 4,870,268 of Vincent et al. for COLOR COMBINER AND SEPARATOR AND IMPLEMENTATIONS; U.S. Pat. No. 4,926,041 of Boyd for OPTICAL SCANNER (and corresponding EPO patent no. 0410578); U.S. Pat. No. 5,019,703 of Boyd et al. for OPTICAL SCANNER WITH MIRROR MOUNTED OCCLUDING APERTURE OR FILTER (and corresponding EPO patent no. 0438868); U.S. Pat. No. 5,032,004 of Steinle for BEAM SPLITTER APPARATUS WITH ADJUSTABLE IMAGE FOCUS AND REGISTRATION (and corresponding EPO patent no. 0458492); 5,044,727 of Steinle for BEAM SPLITTER/COMBINER APPARATUS (and corresponding EPO patent no. 0455450); U.S. Pat. No. 5,040,872 of Steinle for BEAM SPLITTER/COMBINER WITH PATH LENGTH COMPENSATOR; 5,227,620 of Elder, Jr. et al. for APPARATUS FOR ASSEMBLING COMPONENTS OF COLOR OPTICAL SCANNERS (and corresponding EPO patent no. 0576788) and U.S. Pat. No. 5,410,347 of Steinle et al. for COLOR OPTICAL SCANNER WITH IMAGE REGISTRATION HOLDING ASSEMBLY, which are all hereby specifically incorporated by reference for all that is disclosed therein.
In imaging devices and particularly in a line-focus type imaging device as described above, it is preferable for accurate imaging that the light beam from the object be accurately aligned with the photosensor array. In a typical line-focus scanning device, before reaching the photosensor array, the imaging light beam is transmitted by one or more optical components, e.g., a lens. Even a slight mis-alignment between any of these optical components and the photosensor array can cause a serious mis-alignment between the light beam and the photosensor array and result in a corresponding degradation in imaging quality.
Scanning devices that include light beam alignment features are fully described in U.S. Pat. No. 5,646,394 of Steinle et al. for IMAGING DEVICE WITH BEAM STEERING CAPABILITY and in U.S. Pat. No. 6,147,343 of Christensen for PHOTOELECTRIC IMAGING METHOD AND APPARATUS, which are both hereby specifically incorporated by reference for all that is disclosed therein.
Typically, the optical components in an imaging device are mounted within an imaging device housing. The photosensor array is typically mounted to a circuit board, which, in turn, is mounted to the imaging device housing. A lens is also typically mounted within the imaging device housing. The lens serves to focus an image of an object onto the photosensor array. In order for the imaging device to function properly, the focus of the lens must be accurately set.
After an imaging device is assembled, the focus of the lens is generally adjusted. Typically, this is done by adjusting the distance between the lens and the photosensor array, i.e., the image distance of the optical system, until the proper focus is achieved. To accomplish this, imaging devices are commonly provided having a reference surface or surfaces for locating the lens. These reference surfaces typically allow the lens to translate in only one degree of movement, i.e., in directions toward or away from the photosensor array, but prevent the lens from being displaced in other directions. Such displacement, if allowed to occur, would otherwise result in misalignment of the lens with respect to the photosensor array. The reference surfaces, thus, allow the focus of the lens to be adjusted while maintaining the alignment between the lens and the photosensor array. Lens reference surfaces, as outlined above, may, for example, take the form of cylindrical surfaces or v-grooves.
Imaging devices also typically include a bracket or some other retention device to lock the lens in place against the reference surface or surfaces after the focus of the imaging system has been set. The bracket may, for example, be secured by a screw. Accordingly, the screw may be loosened when it is desired to move the lens in order to focus the system, and then tightened to lock the lens in place when the proper focus has been achieved.
Conventional retention devices have proven problematic in that they often result in misalignment of the lens during the focusing operation. With respect to the screw retention bracket described above, for example, if the screw is loosened too much prior to the focusing operation, then the lens may be permitted to rotate away from the reference surface or surfaces, thus resulting in misalignment. Also, it is often difficult to sufficiently tighten the screw to lock down the lens after the focusing operation is complete. As a result, the lens may tend to move out of its focused position, even after it has been locked down. Further, it has been found that the torque applied to tighten the retention screw or screws is sometimes transferred to the lens, causing it to rotate out of alignment.
Conventional retention devices have also proven problematic in that they are not readily conducive to adjustment with an automated focus adjustment apparatus, as is commonly used to set the focus in imaging devices.